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Subject[tip:perf/urgent] perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data
Commit-ID:  4d839dd9e4356bbacf3eb0ab13a549b83b008c21
Gitweb: https://git.kernel.org/tip/4d839dd9e4356bbacf3eb0ab13a549b83b008c21
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 17 May 2019 13:52:33 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 24 May 2019 09:00:11 +0200

perf/ring-buffer: Always use {READ,WRITE}_ONCE() for rb->user_page data

We must use {READ,WRITE}_ONCE() on rb->user_page data such that
concurrent usage will see whole values. A few key sites were missing
this.

Suggested-by: Yabin Cui <yabinc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Cc: mark.rutland@arm.com
Cc: namhyung@kernel.org
Fixes: 7b732a750477 ("perf_counter: new output ABI - part 1")
Link: http://lkml.kernel.org/r/20190517115418.394192145@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/events/ring_buffer.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 4b5f8d932400..7a0c73e4b3eb 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -100,7 +100,7 @@ again:
* See perf_output_begin().
*/
smp_wmb(); /* B, matches C */
- rb->user_page->data_head = head;
+ WRITE_ONCE(rb->user_page->data_head, head);

/*
* We must publish the head before decrementing the nest count,
@@ -496,7 +496,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
perf_event_aux_event(handle->event, aux_head, size,
handle->aux_flags);

- rb->user_page->aux_head = rb->aux_head;
+ WRITE_ONCE(rb->user_page->aux_head, rb->aux_head);
if (rb_need_aux_wakeup(rb))
wakeup = true;

@@ -528,7 +528,7 @@ int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)

rb->aux_head += size;

- rb->user_page->aux_head = rb->aux_head;
+ WRITE_ONCE(rb->user_page->aux_head, rb->aux_head);
if (rb_need_aux_wakeup(rb)) {
perf_output_wakeup(handle);
handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
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